Three-group zoom lenses that include, in order from the object side, a first lens group of negative refractive power, a second lens group of positive refractive power, and a third lens group for use in cameras are known in the prior art. These three-group zoom lenses have become widely used because they are compact and provide favorable correction of aberrations.
Recently, digital cameras and video cameras have rapidly become popular, and these cameras are advantageously small and capable of providing high image quality with small aberrations, including distortion, characteristics similarly desired for previous types of cameras. On the other hand, conditions related to the use of solid state image pickup elements, such as CCD's, must be satisfied that do not pertain to the previous types of cameras.
Auto-focus is almost essential in digital cameras and video cameras and faster focusing is desired in such cameras. Therefore, inner focusing or rear focusing that reduces the weight of the moving lens elements, assures the moving lens elements are close to the camera body, and allows easy driving of the lens elements is frequently used as the focusing mode in zoom lenses for such cameras. For example, Japanese Laid-Open Patent Application 2000-284177 discloses a rear focusing zoom lens for achieving rapid focusing and that provides high resolution images having improved aberration correction.
The desired high image quality and small size of digital cameras and video cameras has led to reducing the pixel size (i.e., area per pixel) of the CCD of the image pickup element. As the pixel size is decreased, greater correction of spherical aberration is demanded in order to achieve the higher resolution required of the zoom lens by reducing the pixel size. However, while the zoom lens described in the above-mentioned Japanese application provides favorable correction of distortion and curvature of field, it is difficult to simultaneously reduce the spherical aberration the desired amount. If plural aspheric lenses are used in the first lens group, which is one approach to solving the problem, distortion, curvature of field and spherical aberration can be simultaneously favorably corrected, but the zoom lens tends to become too large and too expensive to manufacture.